Examples of conventionally known flow rate controllers for controlling the amount of fluid flowing through a fluid channel include those using pulse motors for open/close control of valves.
A flow rate controller using a pulse motor, for example, controls the position of a valve during driving by counting the number of input pulses and, when the driving is stopped, moves the valve back to its original position before the entire flow rate controller comes to a stop. This control allows the valve to be controlled the next time driving starts on the assumption that the valve is at the original position.
If the power fails for any reason during the operation, the flow rate controller would stop without moving the valve back to the original position. Thus, if the operation stops before the valve is moved back to the original position, control for returning the valve to the original position (hereinafter referred to as the “return-to-origin control”) must be performed before the next time driving starts.
An example of the return-to-origin control is a technique disclosed in Patent Document 1.
Patent Document 1 discloses a technique for temporarily stopping a pulse motor upon detection of its malfunction while driving it in such a direction as to close a valve, further driving the pulse motor in such a direction as to close the valve by a predetermined number of pulses before stopping the pulse motor, and finally driving the pulse motor in such a direction as to open the valve by a specified number of pulses before stopping the pulse motor, thereby detecting the origin of the valve.
Patent Document 2 discloses a technique, using a position sensor that outputs different signals based on the operating position of a driven part such as a valve, for driving a pulse motor in a predetermined direction upon activation, sampling signals output from the position sensor for each predetermined angle of motor driving during the driving, recognizing the current valve position from the sampling variation pattern, and setting the origin of the valve based on the recognized current position. This technique can reduce the amount of driving of the pulse motor when the motor is returned to its origin because a change in the position of a driven part such as a valve is followed by the updating of the origin, thus quickly enabling normal control.    Patent Document 1:    Japanese Unexamined Patent Application, Publication No.    Patent Document 2:    Japanese Unexamined Patent Application, Publication No.